Metabolism, excretion, and pharmacokinetics of duloxetine in healthy human subjects

Effect of CYP2D6 genotype on duloxetine serum concentration

Duloxetine is metabolized by cytochrome P450 (CYP)1A2 and CYP2D6. The aim of this study was to investigate the effect of the CYP2D6 genotype on duloxetine serum concentration adjusting for age and sex. Patients were included retrospectively from a therapeutic drug monitoring service. Multiple linear regression analysis was used to investigate the effect of CYP2D6 genotype, age and sex on the duloxetine concentration-to-dose (C/D) ratio. In total, 269 patients were included and assigned to the following genotype-predicted phenotype subgroups: CYP2D6 poor metabolizers (PMs, n = 23), intermediate metabolizers (IMs, n = 121), normal metabolizers (NMs, n = 120) and ultrarapid metabolizers (UMs, n = 5). Multiple linear regression analysis revealed a 95% higher duloxetine C/D ratio in PMs compared with NMs (p = 0.009). Patients ≥65 years had a 56% higher C/D ratio than younger patients (p = 0.01), while women had a 46% higher C/D ratio than men (p = 0.04). In conclusion, the CYP2D6 PM phenotype is associated with a twofold higher concentration at recommended dosing compared with the NM phenotype. CYP2D6 PM females above 65 years are at particular risk of high duloxetine levels as they may obtain a threefold higher C/D ratio compared with younger, male NMs.

Exploring Enzymatic Hydrolysis of Urine Samples for Investigation of Drugs Associated with Drug-Facilitated Sexual Assault

Analyzing urine is common in drug-facilitated sexual assault cases if the analysis of blood is not optimal. The efficient enzymatic pretreatment of urine is important for cleaving glucuronides and improving the detection of the parent drug. The aim was to investigate the efficiency of three β-glucuronidases on eleven glucuronides relevant to DFSA at different incubation periods and temperatures. Human drug-free urine was fortified with 11 glucuronides, hydrolyzed with either β-glucuronidase/arylsulfatase (Helix Pomatia), recombinant β-glucuronidase B-One™ or recombinant β-glucuronidase BGTurbo™ and incubated for 5, 10, 60 min, 18 h and 24 h at 20 °C/40 °C/55 °C before UHPLC-MS/MS analysis. The stability of 141 drugs and metabolites relevant to DFSA was investigated by incubating fortified urine under the same hydrolysis conditions. B-One™ showed efficient hydrolysis (>90%) of most glucuronides in 5 min at all temperatures, while BGTurbo™ showed a similar efficiency (>90%), but the optimal temperature (20-55 °C) and incubation time (5-60 min) varied among analytes. The β-glucuronidase/arylsulfatase had the lowest efficiency and required the longest incubation (24 h) at 40-55 °C. The stability of 99% of 141 drugs and metabolites was not affected by incubation at 20-55 °C for 24 h. Recombinant enzymes show promising results for the simple and efficient hydrolysis of a broad panel of glucuronides relevant for DFSA.

Antidepressant pharmaceuticals in aquatic systems, individual-level ecotoxicological effects: growth, survival and behavior

The growing consumption of antidepressant pharmaceuticals has resulted in their widespread occurrence in the environment, particularly in waterways with a typical concentration range from ng L^-1 to μg L^-1. An increasing number of studies have confirmed the ecotoxic potency of antidepressants, not only at high concentrations but also at environmentally relevant levels. The present review covers literature from the last decade on the individual-level ecotoxicological effects of the most commonly used antidepressants, including their impact on behavior, growth, and survival. We focus on the relationship between antidepressants physico-chemical properties and dynamics in the environment. Furthermore, we discuss the advantages of considering behavioral changes as sensitive endpoints in ecotoxicology, as well as some current methodological shortcomings in the field, including low standardization, reproducibility and context-dependency.

The roles of Cyp1a2 and Cyp2d in pharmacokinetic profiles of serotonin and norepinephrine reuptake inhibitor duloxetine and its metabolites in mice

Duloxetine (DLX) is widely used to treat major depressive disorder. Little is known about the mechanistic basis for DLX-related adverse effects (e.g., liver injury). Human CYP1A2 and CYP2D6 mainly contributes to DLX metabolism, which was proposed to be involved in its adverse effects. Here, we investigated the roles of Cyp1a2 and Cyp2d on DLX pharmacokinetic profile and tissue distribution using a Cyp1a2 knockout (Cyp1a2-KO) mouse model together with a Cyp2d inhibitor (propranolol). Cyp1a2-KO has the few effects on the systematic exposure (area under the plasma concentration-time curve, AUC) and tissue disposition of DLX and its primary metabolites. Propranolol dramatically increased the AUCs of DLX by 3 folds and 1.5 folds in WT and Cyp1a2-KO mice, respectively. Meanwhile, Cyp2d inhibitor decreased the AUC of Cyp2d-involved DLX metabolites (e.g., M16). Mouse tissue distribution revealed that DLX and its major metabolites were the most abundant in kidney, followed by liver and lung with/without Cyp2d inhibitor. Cyp2d inhibitor significantly increased DLX levels in tissues (e.g., liver) in WT and KO mice and decreases the levels of M3, M15, M16 and M17, while it increased the levels of M4, M28 and M29 in tissues. Our findings indicated that Cyp2d play a fundamental role on DLX pharmacokinetic profile and tissue distribution in mice. Clinical studies suggested that CYP1A2 has more effects on DLX systemic exposure than CYP2D6. Further studies in liver humanized mice or clinical studies concerning CYP2D6 inhibitors-DLX interaction study could clarify the roles of CYP2D6 on DLX pharmacokinetics and toxicity in human.

Strategies for Assessing Acceptable Intakes for Novel N-Nitrosamines Derived from Active Pharmaceutical Ingredients

The detection of N-nitrosamines, derived from solvents and reagents and, on occasion, the active pharmaceutical ingredient (API) at higher than acceptable levels in drug products, has led regulators to request a detailed review for their presence in all medicinal products. In the absence of rodent carcinogenicity data for novel N-nitrosamines derived from amine-containing APIs, a conservative class limit of 18 ng/day (based on the most carcinogenic N-nitrosamines) or the derivation of acceptable intakes (AIs) using structurally related surrogates with robust rodent carcinogenicity data is recommended. The guidance has implications for the pharmaceutical industry given the vast number of marketed amine-containing drugs. In this perspective, the rate-limiting step in N-nitrosamine carcinogenicity, involving cytochrome P450-mediated α-carbon hydroxylation to yield DNA-reactive diazonium or carbonium ion intermediates, is discussed with reference to the selection of read-across analogs to derive AIs. Risk-mitigation strategies for managing putative N-nitrosamines in the preclinical discovery setting are also presented.

Human Apparent Volume of Distribution Predicts Bioaccumulation of Ionizable Organic Chemicals in Zebrafish Embryos

Chemicals with elevated bioaccumulation profiles present potential hazards to public health and the environment. Ionizable organic compounds (IOCs) increasingly represent a large proportion of commercial chemicals; however, historical approaches for bioaccumulation determinations are mainly developed for neutral chemicals, which were not appropriate for IOCs. Herein, we employed the zebrafish embryo, a common vertebrate model in environmental and biomedical studies, to elucidate toxicokinetics and bioconcentration of eight IOCs with diverse physicochemical properties and pharmacokinetic parameters. At an environmentally relevant pH (7.5), most IOCs exhibited rapid uptake and depuration in zebrafish, suggesting the ionized forms of IOCs are readily bioavailable. Bioconcentration factors (BCF) of these IOCs ranged from 0.0530 to 250 L·kg^-1 wet weight. The human pharmacokinetic proportionality factor, apparent volume of distribution (V_D), better predicted the BCF of selected IOCs than more commonly used hydrophobicity-based parameters (e.g., pH-dependent octanol-water distribution ratio, D_ow). Predictive bioaccumulation models for IOCs were constructed and validated using V_D alone or with D_ow. Significant relationships between fish BCF and human V_D, which is readily available for pharmaceuticals, highlighted the utility of biologically based "read-across" approaches for predicting bioaccumulative potential of IOCs. Our novel findings thus provided an understanding of the partitioning behavior and improved predictive bioconcentration modeling for IOCs.

The role of cytochromes P450 in metabolism of selected antidepressants and anxiolytics under psychological stress

In today's modern society, it seems to be more and more challenging to cope with life stresses. The effect of psychological stress on emotional and physical health can be devastating, and increased stress is associated with increased rates of heart attack, hypertension, obesity, addiction, anxiety and depression. This review focuses on the possibility of an influence of psychological stress on the metabolism of selected antidepressants (TCAs, SSRIs, SNRIs, SARIs, NDRIs a MMAs) and anxiolytics (benzodiazepines and azapirone), as patients treated with antidepressants and/or anxiolytics can still suffer from psychological stress. Emphasis is placed on the drug metabolism mediated by the enzymes of Phase I, typically cytochromes P450 (CYPs), which are the major enzymes involved in drug metabolism, as the majority of psychoactive substances are metabolized by numerous CYPs (such as CYP1A2, CYP2B6, CYP2C19, CYP2C9, CYP2A6, CYP2D6, CYP3A4). As the data on the effect of stress on human enzymes are extremely rare, modulation of the efficacy and even regulation of the biotransformation pathways of drugs by psychological stress can be expected to play a significant role, as there is increasing evidence that stress can alter drug metabolism, hence there is a risk of less effective drug metabolism and increased side effects.

Metabolism of a Selective Serotonin and Norepinephrine Reuptake Inhibitor Duloxetine in Liver Microsomes and Mice

Duloxetine (DLX) is a dual serotonin and norepinephrine reuptake inhibitor, widely used for the treatment of major depressive disorder. Although DLX has shown good efficacy and safety, serious adverse effects (e.g., liver injury) have been reported. The mechanisms associated with DLX-induced toxicity remain elusive. Drug metabolism plays critical roles in drug safety and efficacy. However, the metabolic profile of DLX in mice is not available, although mice serve as commonly used animal models for mechanistic studies of drug-induced adverse effects. Our study revealed 39 DLX metabolites in human/mouse liver microsomes and mice. Of note, 13 metabolites are novel, including five N-acetyl cysteine adducts and one reduced glutathione (GSH) adduct associated with DLX. Additionally, the species differences of certain metabolites were observed between human and mouse liver microsomes. CYP1A2 and CYP2D6 are primary enzymes responsible for the formation of DLX metabolites in liver microsomes, including DLX-GSH adducts. In summary, a total of 39 DLX metabolites were identified, and species differences were noticed in vitro. The roles of CYP450s in DLX metabolite formation were also verified using human recombinant cytochrome P450 (P450) enzymes and corresponding chemical inhibitors. Further studies are warranted to address the exact role of DLX metabolism in its adverse effects in vitro (e.g., human primary hepatocytes) and in vivo (e.g., Cyp1a2-null mice). SIGNIFICANCE STATEMENT: This current study systematically investigated Duloxetine (DLX) metabolism and bioactivation in liver microsomes and mice. This study provided a global view of DLX metabolism and bioactivation in liver microsomes and mice, which are very valuable to further elucidate the mechanistic study of DLX-related adverse effects and drug-drug interaction from metabolic aspects.

Simultaneous determination of duloxetine and 4-hydroxy duloxetine glucuronide in human plasma and back-conversion study

Aim: To develop an LC-MS/MS method for simultaneous determination of duloxetine and its metabolite, 4-hydroxy duloxetine glucuronide (4HDG) in human plasma and to investigate the potential back-conversion of 4HDG to duloxetine using stability study. Materials & methods: The LC-MS/MS method was validated according to the EMA and USFDA Bioanalytical Method Validation Guidelines and applied to pilot bioequivalence study. Results & conclusion: The method validation results were within the acceptance limits. The stability study and incurred sample reanalysis results ruled out the occurrence of back-conversion. The study highlighted the conduct of back-conversion test and the advantages of LC-MS/MS method in terms of sensitivity, specificity and low consumption of organic solvents.

Tools for optimising pharmacotherapy in psychiatry (therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests): focus on antidepressants

Objectives: More than 40 drugs are available to treat affective disorders. Individual selection of the optimal drug and dose is required to attain the highest possible efficacy and acceptable tolerability for every patient.Methods: This review, which includes more than 500 articles selected by 30 experts, combines relevant knowledge on studies investigating the pharmacokinetics, pharmacodynamics and pharmacogenetics of 33 antidepressant drugs and of 4 drugs approved for augmentation in cases of insufficient response to antidepressant monotherapy. Such studies typically measure drug concentrations in blood (i.e. therapeutic drug monitoring) and genotype relevant genetic polymorphisms of enzymes, transporters or receptors involved in drug metabolism or mechanism of action. Imaging studies, primarily positron emission tomography that relates drug concentrations in blood and radioligand binding, are considered to quantify target structure occupancy by the antidepressant drugs in vivo. Results: Evidence is given that in vivo imaging, therapeutic drug monitoring and genotyping and/or phenotyping of drug metabolising enzymes should be an integral part in the development of any new antidepressant drug.Conclusions: To guide antidepressant drug therapy in everyday practice, there are multiple indications such as uncertain adherence, polypharmacy, nonresponse and/or adverse reactions under therapeutically recommended doses, where therapeutic drug monitoring and cytochrome P450 genotyping and/or phenotyping should be applied as valid tools of precision medicine.

Characterization of Phase I Hepatic Metabolites of Anti-Premature Ejaculation Drug Dapoxetine by UHPLC-ESI-Q-TOF

Determination of the metabolism pathway of xenobiotics undergoing the hepatic pass is a crucial aspect in drug development since the presence of toxic biotransformation products may result in significant side effects during the therapy. In this study, the complete hepatic metabolism pathway of dapoxetine established according to the human liver microsome assay with the use of a high-resolution LC-MS system was described. Eleven biotransformation products of dapoxetine, including eight metabolites not reported in the literature so far, were detected and identified. N-dealkylation, hydroxylation, N-oxidation and dearylation were found to be the main metabolic reactions for the investigated xenobiotic. In silico analysis of toxicity revealed that the reaction of didesmethylation may contribute to the increased carcinogenic potential of dapoxetine metabolites. On the other hand, N-oxidation and aromatic hydroxylation biotransformation reactions possibly lead to the formation of mutagenic compounds.

Therapy response prediction in major depressive disorder: current and novel genomic markers influencing pharmacokinetics and pharmacodynamics

Major depressive disorder is connected with high rates of functional disability and mortality. About a third of the patients are at risk of therapy failure. Several pharmacogenetic markers especially located in CYP450 genes such as CYP2D6 or CYP2C19 are of relevance for therapy outcome prediction in major depressive disorder but a further optimization of predictive tools is warranted. The article summarizes the current knowledge on pharmacogenetic variants, therapy effects and side effects of important antidepressive therapeutics, and sheds light on new methodological approaches for therapy response estimation based on genetic markers with relevance for pharmacokinetics, pharmacodynamics and disease pathology identified in genome-wide association study analyses, highlighting polygenic risk score analysis as a tool for further optimization of individualized therapy outcome prediction.

First-in-human safety, tolerability, and pharmacokinetics of ammoxetine in healthy subjects: a randomized, double-blind, placebo-controlled phase I study

BACKGROUND

Ammoxetine is a novel selective serotonin and norepinephrine reuptake inhibitor. Preclinical studies have indicated the potential utility of ammoxetine for therapy in major depressive disorder.

PURPOSE

To investigate the first-in-human safety, tolerability, and pharmacokinetics (PK) of ammoxetine in healthy subjects and evaluate the effect of CYP2C19 polymorphisms on metabolism of ammoxetine.

METHODS

In this randomized, double-blind, placebo-controlled phase I study, healthy Chinese subjects were allocated to receive 2.5, 7.5, 15, 30, 45, 65, 100 mg ammoxetine or placebo in single-dose part and 15, 30, 45 mg ammoxetine or placebo twice daily for 8 days in multiple-dose part. Pharmacokinetic, safety and tolerability assessments were performed.

RESULTS

A total of 134 subjects were screened and 94 were enrolled. All the ammoxetine-related adverse events (AEs) were mild and resolved spontaneously. No hepatic AEs were reported during the study. Ammoxetine was well absorbed after oral administration with T_max reached in 5.0-6.0 h. After single-dosing, C_max and AUC increased proportionally with dose, except at 65 mg. After multiple-dosing, the exposures of ammoxetine at steady state increased slightly in a more-than-dose-proportional manner over the dose range studied, probably due to the saturated elimination. Steady state was achieved 6 days after multiple-dosing was initiated. The low extent of urinary excretion of ammoxetine (< 2%) indicated it is undergoing extensive metabolism. CYP2C19 polymorphisms had minimal effect on metabolism of ammoxetine.

CONCLUSIONS

Ammoxetine has a favorable pharmacokinetic profile after oral administration and good safety properties. The PK and safety profiles of ammoxetine could enable further clinical development in patients with major depressive disorder.

Genotoxic and oxidative effect of duloxetine on mouse brain and liver tissues

We evaluated the duloxetine DNA damaging capacity utilizing the comet assay applied to mouse brain and liver cells, as well as its DNA, lipid, protein, and nitric oxide oxidative potential in the same cells. A kinetic time/dose strategy showed the effect of 2, 20, and 200 mg/kg of the drug administered intraperitoneally once in comparison with a control and a methyl methanesulfonate group. Each parameter was evaluated at 3, 9, 15, and 21 h postadministration in five mice per group, except for the DNA oxidation that was examined only at 9 h postadministration. Results showed a significant DNA damage mainly at 9 h postexposure in both organs. In the brain, with 20 and 200 mg/kg we found 50 and 80% increase over the control group (p ≤ 0.05), in the liver, the increase of 2, 20, and 200 mg/kg of duloxetine was 50, 80, and 135% in comparison with the control level (p ≤ 0.05). DNA, lipid, protein and nitric oxide oxidation increase was also observed in both organs. Our data established the DNA damaging capacity of duloxetine even with a dose from the therapeutic range (2 mg/kg), and suggest that this effect can be related with its oxidative potential.

Tissue and interspecies comparison of catechol-O-methyltransferase mediated catalysis of 6-O-methylation of esculetin to scopoletin and its inhibition by entacapone and tolcapone

Catechol-O-methyltransferase (COMT) methylates both endogenous and exogenous catechol compounds to inactive and safe metabolites. We first optimised conditions for a convenient and sensitive continuous fluorescence-based 6-O-methylation assay of esculetin, which we used for investigating the COMT activity in human, mouse, rat, dog, rabbit, and sheep liver cytosols and microsomes and in ten different rat tissues. Furthermore, we compared the inhibition potencies and mechanisms of two clinically used COMT inhibitors, entacapone and tolcapone, in these species. In most tissues, the COMT activity was at least three times higher in cytosol than in microsomes. In the rat, the highest COMT activity was found in the liver, followed by kidney, ileum, thymus, spleen, lung, pancreas, heart, brain, and finally, skeletal muscle. Entacapone and tolcapone were characterised as highly potent mixed type tight-binding inhibitors. The competitive inhibition type dominated over the uncompetitive inhibition with entacapone, whereas uncompetitive inhibition dominated with tolcapone. Rats, dogs, pigs, and sheep are high COMT activity species, in contrast to humans, mice, and rabbits; COMT activity is highest in the liver. Both entacapone and tolcapone are potent COMT inhibitors, but their inhibition mechanisms differ.

Metabolic profiling of norepinephrine reuptake inhibitor atomoxetine

Atomoxetine (ATX), a selective and potent inhibitor of the presynaptic norepinephrine transporter, is used mainly to treat attention-deficit hyperactivity disorder. Although multiple adverse effects associated with ATX have been reported including severe liver injuries, the mechanisms of ATX-related toxicity remain largely unknown. Metabolism frequently contributes to adverse effects of a drug through reactive metabolites, and the bioactivation status of ATX is still not investigated yet. Here, we systematically investigated ATX metabolism, bioactivation, species difference in human, mouse, and rat liver microsomes (HLM, MLM, and RLM) and in mice using metabolomic approaches as mice and rats are commonly used animal models for the studies of drug toxicity. We identified thirty one ATX metabolites and adducts in LMs and mice, 16 of which are novel. In LMs, we uncovered two methoxyamine-trapped aldehydes, two cyclization metabolites, detoluene-ATX, and ATX-N-hydroxylation for the first time. Detoluene-ATX and one cyclization metabolite were also observed in mice. Using chemical inhibitors and recombinant CYP enzymes, we demonstrated that CYP2C8 and CYP2B6 mainly contribute to the formation of aldehyde; CYP2D6 is the dominant enzyme for the formation of ATX cyclization and detoluene-ATX; CYP3A4 is major enzyme responsible for the hydroxylamine formation. The findings concerning aldehydes should be very useful to further elucidate the mechanistic aspects of adverse effects associated with ATX from metabolic angles. Additionally, the species differences for each metabolite should be helpful to investigate the contribution of specific metabolites to ATX toxicity and possible drug-drug interactions in suitable models.

Achiral and chiral analysis of duloxetine by chromatographic and electrophoretic methods, a review on the separation methodologies

Duloxetine (DLX) is a widely used antidepressant drug belonging to the class of selective serotonin and norepinephrine reuptake inhibitors (SNRIs); its efficacy has been demonstrated in the treatment of not only major depressive disorders but also diabetic neuropathic pain, generalized anxiety disorder, fibromyalgia or stress urinary incontinence. It is a chiral substance and is used in therapy in the form of the enantiopure S-DLX, which is twice as active as R-DLX. Several methods have been published for the achiral and chiral determination of DLX in pharmaceuticals, biological materials and environmental samples, the majority using liquid chromatography and capillary electrophoresis coupled with different detection techniques (UV detection, fluorescence, mass spectrometry). The aim of the current review is to provide a systematic survey of the analytical techniques used for the determination of DLX from different matrices.

Application of an Inter-Species Extrapolation Method for the Prediction of Drug Interactions between Propolis and Duloxetine in Humans

Duloxetine (DLX) is a potent drug investigated for the treatment of depression and urinary incontinence. DLX is extensively metabolized in the liver by two P450 isozymes, CYP2D6 and CYP1A2. Propolis (PPL) is one of the popular functional foods known to have effects on activities of CYPs, including CYP1A2. Due to the high probability of using DLX and PPL simultaneously, the present study was designed to investigate the potent effect of PPL on pharmacokinetics (PKs) of DLX after co-administration in humans. A PK study was first conducted in 18 rats (n = 6/group), in which the plasma concentration of DLX and its major metabolite 4-hydroxy duloxetine (4-HD) with or without administration of PPL was recorded. Population PKs and potential effects of PPL were then analyzed using NONMEM software. Lastly, these results were extrapolated from rats to humans using the allometric scaling and the liver blood flow method. PPL (15,000 mg/day) exerts a statistically significant increase in DLX exposures at steady state, with a 20.2% and 24.6% increase in DLX C m a x , s s and the same 28.0% increase in DLX A U C s s when DLX (40 or 60 mg) was administered once or twice daily, respectively. In conclusion, safety issues are required to be attended to when individuals simultaneously use DLX and PPL at high doses, and the possibility of interactions between DLX and PPL might be noted.

The Effect of Food on the Single-Dose Bioavailability and Tolerability of the Highest Marketed Strength of Duloxetine

Duloxetine is a combined serotonin and norepinephrine reuptake inhibitor indicated in adults for the treatment of major depressive disorder, diabetic peripheral neuropathic pain, and generalized anxiety disorder. The aim of these studies was to evaluate the effect of food on the pharmacokinetics and safety of duloxetine 60‐mg gastroresistant hard capsules following single‐dose administration. The data were obtained from 2 phase 1 bioequivalence studies, 1 in a fasting state and the other under fed conditions. Both studies have shown that, when administered as a single dose in the same prandial state, the test and reference duloxetine treatments were bioequivalent and exhibited similar safety profiles. The mean fed and fasting pharmacokinetic parameters and drug‐related adverse events from the 2 studies were compared in order to assess the effect of food on the duloxetine bioavailability and respectively, tolerability. Administration of duloxetine in fed conditions increased peak plasma concentration by up to 30% and delayed mean time to peak concentration by an average of 1.15 hours while having an insignificant effect on extent of absorption (area under the plasma concentration–time curve in fed state within ±6% as compared with fasting conditions). Even though peak plasma levels were substantially higher in the fed state, there was no negative impact on the drug's safety profile. Actually, administration with food resulted in a lower average number of adverse events per single dose exposure. The negligible variation in overall systemic exposure suggests that efficacy remains unchanged irrespective of administration conditions; however, a better tolerability of the 60‐mg dose is expected when the drug is taken with food.

Designing around Structural Alerts in Drug Discovery

Cumulative research over several decades has implicated the involvement of reactive metabolites in many idiosyncratic adverse drug reactions (IADRs). Consequently, "avoidance" strategies have been inserted into drug discovery paradigms, which include the exclusion of structural alerts and possible termination of reactive metabolite-positive compounds. Several noteworthy examples where reactive metabolite-related liabilities have been resolved through structure-metabolism studies are presented herein. Considerable progress has also been made in addressing the limitations of the avoidance strategy and further refining the process of managing reactive metabolite issues in drug development. These efforts primarily stemmed from the observation that numerous drugs, which contain structural alerts and/or form reactive metabolites, are devoid of ADRs. The Perspective also dwells into an analysis of the structural alert/reactive metabolite concept with a discussion of risk mitigation tactics to support the progression of reactive metabolite-positive drug candidates.

Development and Evaluation of Optimized Thiolated Chitosan Proniosomal Gel Containing Duloxetine for Intranasal Delivery

Proniosomes offer excellent potential for improved drug delivery, through versatile routes, by overcoming the permeation barriers faced by several drugs. The study was aimed to develop a thiomer gel containing duloxetine proniosomes for the intranasal delivery, improving its bioavailability and brain delivery through olfactory system. Duloxetine-loaded proniosomes were optimized through Design-Expert Software, prepared by coacervation phase separation method and then characterized in vitro for different vesicle features, and permeation enhancement potential using various techniques. The formulation F2, out of all the trials, fulfilled the maximum requisite of highest entrapment efficiency (76.21 ± 1.24%) and minimum vesicle size (223.91 ± 11.07 nm). The F2 was embedded in thiolated chitosan gel rendering it mucoadhesive and further characterized. The in vitro release showed a sustained drug release from the mucoadhesive proniosomal gel with only 54% drug release as compared to that of 71% from proniosome over 8 h, following Higuchi drug release model. Ex vivo permeation studies showed the enhancement ratio for the mucoadhesive proniosomal gel to be 1.86-fold greater than proniosomes, indicating a significant improvement in transmucosal permeation. The results suggest that incorporation of proniosomes into thiolated gel can significantly improve its mucoadhesion and retention time in the nasal cavity for providing a sustained drug release. Thus, gel formulation could be considered as a promising approach for efficient intranasal drug delivery of duloxetine. Graphical Abstract.

A Randomized, Double-Blind, Placebo- and Active Comparator-Controlled Phase I Study of Analgesic/Antihyperalgesic Properties of ASP8477, a Fatty Acid Amide Hydrolase Inhibitor, in Healthy Female Subjects

Objectives

To evaluate the analgesic/antihyperalgesic effect of ASP8477.

Design

Randomized, double-blind, double-dummy, cross-over, placebo- and active comparator-controlled study.

Setting

HPR Dr. Schaffler GmbH, Munich, Germany.

Subjects

Healthy female subjects aged 18–65 years.

Methods

Eligible subjects were randomly assigned to one of six treatment sequences and received multiple ascending doses of ASP8477, duloxetine, and placebo over three treatment periods (each consisting of 21-day dosing separated by 14-day washout periods). On the last day of each dose level, laser evoked potentials (LEPs) and visual analog scales (VAS pain) on capsaicin-treated skin at baseline and at multiple postdose time points were assessed. The primary end point was the difference in LEP N2-P2 peak-to-peak (PtP) amplitudes for ASP8477 100 mg vs placebo.

Results

Twenty-five subjects were randomized. In all subjects, LEP N2-P2 PtP amplitudes were numerically lower for ASP8477 100 mg vs placebo (P = 0.0721); in subjects who demonstrated positive capsaicin skin effects, a greater mean difference of –2.24 µV (P = 0.0146) was observed. Across all doses, LEP N2-P2 PtP amplitudes were lower for duloxetine compared with ASP8477 (mean difference –3.80 µV; P < 0.0001) or placebo (mean difference –5.21 µV; P < 0.0001). The effect of ASP8477 (all doses) on down-scoring the VAS pain score was significant compared with placebo (mean difference –2.55%; P < 0.0007).

Conclusions

ASP8477 was well tolerated in this study. Analysis of all subjects did not demonstrate a significant difference in LEP for ASP8477 100 mg over placebo but did in subjects who demonstrated positive capsaicin skin effects.

Antidepressants and nose-to-brain delivery: drivers, restraints, opportunities and challenges

Why is nose-to-brain delivery considered to be a strategy that directly allows the access of antidepressants to the brain? In which circumstances can the intranasal pathway be applicable? Are there any requirements to follow? What triggers the antidepressant market? Which constraints are imposed during discovery programs? What opportunities can arise and what is their current status of development? Are they already translated into clinical practice? Which challenges are expected from recent development strategies? This review aims at providing a critical appraisal of nose-to-brain delivery of antidepressants, framed within a comprehensive analysis of drivers, restraints, opportunities and challenges.

Validated Microemulsion Liquid Chromatography-Fluorescence Method for the Quantification of Duloxetine and its Two Main Metabolites in Plasma: Application to Clinical Pharmacokinetic Studies

Background:

Duloxetine (DL) is a selective serotonin and norepinephrine reuptake inhibitor. The drug is used in the treatment of major depression, anxiety, pain related to diabetic peripheral neuropathy and stress urinary incontinence. </P><P> Objective: This study described, for the first time, the development and validation of a highly selective and sensitive microemulsion liquid chromatography-fluorescence (MELC-FL) method with low environmental pollution and without extraction steps for the simultaneous quantification of DL, and its two main metabolites; 5-hydroxy-6-methoxy duloxetine (5-HDL) and 4-hydroxy duloxetine glucuronide (4- HDLG) in plasma.

Methods:

The studied analytes and methyl paraben (an internal standard) were detected using excitation and emission wavelengths of 280 and 340 nm, respectively. The analysis was performed on Water Symmetry C18 analytical column (100 Å, 150 mm x 3.9 mm, 5 µm) by directly injecting the plasma after appropriate dilution with microemulsion mobile phase. Total analytical run time was 4 min.

Results:

The MELC-FL method was statistically validated according to the FDA guidelines for bioanalytical methods for linearity, accuracy, precision, specificity, robustness, and stability. Linear calibration plots were achieved in the ranges of 25-1200 ng/mL for DL and 50-1500 ng/mL for 5-HDL and 4- HDLG (r2 ≥ 0.997) in rat plasma. The intra- and inter- assay precisions and accuracy were acceptable. The overall recoveries of DL and its two main metabolites from rat plasma were between 97.12% and 103.12% with an RSD value between 0.34% and 4.57%.

Conclusion:

The present study supports the possible use of the microemulsion mobile phase in LC as a “greener ” mobile phase. The developed method offered an advantage in the form of direct analysis of biological samples after appropriate dilution with eco-friendly microemulsion mobile phase, which decreased the possibility of sample loss during analysis. The developed assay was successfully applied in a pharmacokinetic study and it established the applicability of the method for the determination of concentration-time profiles of DL and its two main metabolites in rat plasma after systemic administration.

Duloxetine in Psychiatric Disorders: Expansions Beyond Major Depression and Generalized Anxiety Disorder

Background: Duloxetine hydrochloride (DUL) is an antidepressant included in the pharmacological class of serotonin-norepinephrine reuptake inhibitors approved for the treatment of major depressive disorder, generalized anxiety disorder, diabetic peripheral neuropathic pain, fibromyalgia, and chronic musculoskeletal pain. The aim of this review was to elucidate current evidences on the use of DUL in the treatment of a variety of psychiatric disorders. Methods: This systematic review was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. PubMed database was searched from January 1, 2003, to September 30, 2018, using 11 key terms related to psychiatric disorders ("persistent depressive disorder," "dysthymic disorder," "bipolar disorder," "seasonal affective disorder," "obsessive-compulsive disorder," "social phobia," "panic disorder," "posttraumatic stress disorder," "schizophrenia," "eating disorders," "sexual disorders," "personality disorders") and one key term related to duloxetine ("duloxetine hydrochloride"). Article titles and abstracts were scanned to determine relevance to the topic. For additional studies, the authors also examined the reference lists of several of the included papers. Results: Duloxetine may be an effective treatment for mood spectrum disorders, panic disorder, several symptom clusters of borderline personality, and as add-on drug in schizophrenia. Modest or conflicting results have been found for the efficacy of duloxetine in obsessive-compulsive disorder, posttraumatic stress disorder, eating, and sexual disorders. Conclusion: Major limitations of the reviewed studies were short trial duration, small sample sizes, and the lack of control groups. Defining the potential role of DUL in the treatment of psychiatric disorders other than major depressive disorder and generalized anxiety disorder needs further randomized, placebo-controlled studies.

Does obtaining CYP2D6 and CYP2C19 pharmacogenetic testing predict antidepressant response or adverse drug reactions?

Treatment non-response and adverse reactions are common in patients receiving antidepressants. Personalizing psychiatric treatment based on pharmacogenetic testing has been proposed to help clinicians guide antidepressant selection and dosing. This systematic literature review assesses the two most robustly studied drug-metabolizing enzymes, CYP2D6 and CYP2C19, and examines whether obtaining CYP2D6 and CYP2C19 testing can be used to predict antidepressant response or adverse drug reactions in order to improve clinical outcomes. In general, literature reviews published prior to 2013 indicated that results have been inconsistent linking CYP2D6 and CYP2C19 to antidepressant treatment outcomes, suggesting that more evidence is required to support the clinical implementation of genotyping to predict outcomes. We thus performed an extensive and systematic literature review, focusing on studies published from 2013 through 2018. Sixteen studies were found to be relevant. The results yielded inconsistent findings, suggesting that CYP2D6 and CYP2C19 testing may predict response in certain individuals, but it remains unclear if this will translate to improved clinical outcomes. Further research is required to determine when pharmacogenetic testing should be utilized and in which populations it is indicated. Randomized, controlled, prospective trials with adequate sample sizes would best clarify whether genotype-guided antidepressant selection will ultimately improve clinical outcomes.

Discovery of thiophene-containing biaryl amide derivatives as novel glucagon receptor antagonists

A novel series of thiophene-containing biaryl amide glucagon receptor (GCGR) antagonists were designed and synthesized. Two compounds of this series, 14f and 14h, exhibited good GCGR binding (IC₅₀  = 6.1 and 4.4 μm, respectively) and cAMP functional activities (IC₅₀  = 4.4 and 14.4 μm, respectively). The possible binding modes of compounds 14f and 14h with GCGR were explored by molecular simulation.

Duloxetine in Painful Diabetic Neuropathy: A Systematic Review

OBJECTIVE

To systematically review the evidence for duloxetine in the management of painful diabetic neuropathy (PDN).

METHODS

Electronic searches of Medline and PubMed were performed from 2005 till October 2015 using medical subject headings and free-text words. Two independent reviewers extracted the data and assessed the methodological quality of the selected studies.

RESULTS

Twenty-three studies met our inclusion criteria and 8 were considered of high quality and were included to this review. Because of heterogeneity of the studies included in this review, statistical pooling of the data was not possible. We found good evidence for use of duloxetine in PDN over placebo and pregabalin but there was no benefit of duloxetine over amitriptyline.

CONCLUSIONS

Duloxetine has a beneficial effect over placebo. Nevertheless, the evidence of superiority of duloxetine over pregabalin and amitriptyline should be explored further as there was only 1 trial for each category. Provided majority of the PDN patients share cardiovascular complications, use of duloxetine will be a good option for treating pain associated with PDN over amitriptyline. Future randomized controlled trials should be designed keeping this in mind.

Inhibition of Cytochrome P450 by Propolis in Human Liver Microsomes

Although propolis is one of the most popular functional foods for human health, there have been no comprehensive studies of herb-drug interactions through cytochrome P450 (CYP) inhibition. The purpose of this study was to determine the inhibitory effects of propolis on the activities of CYP1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1 and 3A4 using pooled human liver microsomes (HLMs). Propolis inhibited CYP1A2, CYP2E1 and CYP2C19 with an IC₅₀ value of 6.9, 16.8, and 43.1 μg/mL, respectively, whereas CYP2A6, 2B6, 2C9, 2D6, and 3A4 were unaffected. Based on half-maximal inhibitory concentration shifts between microsomes incubated with and without nicotinamide adenine dinucleotide phosphate, propolis-induced CYP1A2, CYP2C19, and CYP2E1 inhibition was metabolism-independent. To evaluate the interaction potential between propolis and therapeutic drugs, the effects of propolis on metabolism of duloxetine, a serotonin-norepinephrine reuptake inhibitor, were determined in HLMs. CYP1A2 and CYP2D6 are involved in hydroxylation of duloxetine to 4-hydroxy duloxetine, the major metabolite, which was decreased following propolis addition in HLMs. These results raise the possibility of interactions between propolis and therapeutic drugs metabolized by CYP1A2.

Comparison of the Anti-tumor Effects of Selective Serotonin Reuptake Inhibitors as Well as Serotonin and Norepinephrine Reuptake Inhibitors in Human Hepatocellular Carcinoma Cells

The anti-tumor effects of selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs) on several types of cancer cells have been reported. However, comparison of the anti-tumor effects of these drugs on human hepatocellular carcinoma (HepG2) cells has not been studied. We compared the anti-tumor effects of four SSRIs and two SNRIs on HepG2 cells. SSRIs and duloxetine dose-dependently decreased cell viability. Milnacipran had no effect on cell viability. The half-maximal inhibitory concentration was lower in the order of: sertraline, paroxetine, duloxetine, fluvoxamine, escitalopram, and milnacipran. Exposure to sertraline (2 µM) significantly increased caspase-3/7 activity. These results suggest that, of the agents tested here, sertraline had the highest sensitivity to HepG2 cells, and activation of the caspase pathway is involved in the anti-tumor effects of sertraline in HepG2 cells.

Duloxetine enters the brain - But why is it not found in the cerebrospinal fluid

BACKGROUND

Antidepressants enter the brain to reach their site of action in a different extent. However, there has been no study to date about duloxetine's ability to enter the brain and cerebrospinal fluid. Aim of this study was to measure blood and cerebrospinal fluid concentrations of duloxetine and to account for the distribution between the two compartments.

METHODS

Concentrations of duloxetine were measured in blood serum and cerebrospinal fluid of 19 patients treated with daily doses of 30-120mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations and serum concentrations were correlated with concentrations in cerebrospinal fluid.

RESULTS

Serum concentrations of duloxetine showed a moderate but significant correlation with the applied daily dose, r=+0.473, p=0.04. Duloxetine concentrations in the cerebrospinal fluid above the designated limit of quantification of 2.0ng/mL were only found in three of the 19 patients.

CONCLUSIONS AND LIMITATIONS

Contrasting to own preceding studies on venlafaxine, mirtazapine and citalopram with comparably high concentrations in cerebrospinal fluid, the here presented findings indicate that duloxetine shows a very different distribution pattern. Very low concentrations in the cerebrospinal fluid may be due to the fact that the drug crosses the blood-cerebrospinal fluid barrier much worse than other antidepressants do, suggesting a low ability of duloxetine to enter the brain. Alternatively, low drug concentrations may be interpreted in a sense of a missing residence time in cerebrospinal fluid due to active transport mechanisms out of this environment either back into the bloodstream or into the brain.

Rapid onset of syndrome of inappropriate antidiuretic hormone secretion induced by duloxetine in an elderly type 2 diabetic patient with painful diabetic neuropathy

Diabetic neuropathy is the most common diabetic complication. Duloxetine, a serotonin noradrenaline reuptake inhibitor (SNRI), is widely used for the treatment of diabetic painful neuropathy (DPN) because of the efficacy and safety profile. Syndrome of inappropriate antidiuretic hormone secretion, which is strongly associated duloxetine, is a rare but occasionally life-threatening adverse effect. Here, we report a case of syndrome of inappropriate antidiuretic hormone secretion that rapidly developed after starting duloxetine in an elderly Japanese female type 2 diabetes mellitus patient. Furthermore, we discuss the possible relationship between the onset of syndrome of inappropriate antidiuretic hormone secretion and the gene polymorphism of cytochrome P450 isoform 1A2 and 2D6, both of which are responsible for duloxetine metabolism.

Serotonin and noradrenaline reuptake inhibitors improve micturition control in mice

Poor micturition control may cause profound distress, because proper voiding is mandatory for an active social life. Micturition results from the subtle interplay of central and peripheral components. It involves the coordination of autonomic and neuromuscular activity at the brainstem level, under the executive control of the prefrontal cortex. We tested the hypothesis that administration of molecules acting as reuptake inhibitors of serotonin, noradrenaline or both may exert a strong effect on the control of urine release, in a mouse model of overactive bladder. Mice were injected with cyclophosphamide (40 mg/kg), to increase micturition acts. Mice were then given one of four molecules: the serotonin reuptake inhibitor imipramine, its metabolite desipramine that acts on noradrenaline reuptake, the serotonin and noradrenaline reuptake inhibitor duloxetine or its active metabolite 4-hydroxy-duloxetine. Cyclophosphamide increased urine release without inducing overt toxicity or inflammation, except for increase in urothelium thickness. All the antidepressants were able to decrease the cyclophosphamide effects, as apparent from longer latency to the first micturition act, decreased number of urine spots and volume of released urine. These results suggest that serotonin and noradrenaline reuptake inhibitors exert a strong and effective modulatory effect on the control of urine release and prompt to additional studies on their central effects on brain areas involved in the social and behavioral control of micturition.

Bioactivation potential of thiophene-containing drugs

Thiophene is a five-membered, sulfur-containing heteroaromatic ring commonly used as a building block in drugs. It is considered to be a structural alert, as its metabolism can lead to the formation of reactive metabolites. Thiophene S-oxides and thiophene epoxides are highly reactive electrophilic thiophene metabolites whose formation is cytochrome P450-dependent. These reactive thiophene-based metabolites are quite often responsible for drug-induced hepatotoxicity. Tienilic acid is an example of a thiophene-based drug that was withdrawn from the market after only a few months of use, due to severe cases of immune hepatitis. However, inclusion of the thiophene moiety in drugs does not necessarily result in toxic effects. The presence of other, less toxic metabolic pathways, as well as an effective detoxification system in our body, protects us from the bioactivation potential of the thiophene ring. Thus, the presence of a structural alert itself is insufficient to predict a compound's toxicity. The question therefore arises as to which factors significantly influence the toxicity of thiophene-containing drugs. There is no easy way to answer this question. However, the findings presented here indicate that, for a number of reasons, daily dose and alternative metabolic pathways are important factors when predicting toxicity and will therefore be discussed together with examples.

Determination of duloxetine in human plasma with proven lack of influence of the major metabolite 4-hydroxyduloxetine

OBJECTIVES

Minimizing the impact of major or unstable metabolites on the determination of a drug substance represents a leading task in the development and validation of bioanalytical methods. "Incurred samples reanalysis" provides relevant information too late; therefore, carefully selected tests on known metabolites should precede the pharmacokinetic studies.

DESIGN AND METHODS

This paper describes a simple and rapid HPLC-UV method for the determination of duloxetine, a potent serotonin and norepinephrine reuptake inhibitor, in the presence of its major metabolite, i.e. 4-hydroxyduloxetine glucuronide. Analyte and fluoxetine (internal standard) were extracted from human plasma by liquid-liquid extraction.

RESULTS

No influence of the major metabolite was observed on the reliability of the new method. There was also lack of evidence of the major metabolite back-conversion to the parent drug substance. The validation demonstrated high precision of the new method. All validation parameters met the acceptance criteria of bioanalytical regulations.

CONCLUSIONS

The new method enabled the reliable determination of duloxetine in the presence of its major metabolite in the human plasma. The method might be applied to pharmacokinetic studies in humans, including bioequivalence and therapeutic drug monitoring.

Pharmacoscintigraphic evaluation of potential of lipid nanocarriers for nose-to-brain delivery of antidepressant drug

Efficacy of antidepressants relies upon their continued presence at the site of action (brain) over a prolonged period of time. The BBB restricts the access of antidepressants to the brain on oral as well as intravenous administration. Direct delivery (by-passing the BBB) of antidepressant drugs can increase the CSF concentration with concomitant reduction in dose and side effects. Intranasal administration of nanostructured lipid carriers (NLC) containing antidepressant drug circumvent the BBB and maintain the prolonged release at the site of action. The aim of the present study was to evaluate the enhancement in brain uptake of NLC containing duloxetine (DLX) after intranasal administration. Duloxetine loaded NLC (DLX-NLC) was evaluated pharmacoscintigraphically for drug targeting potential (DTP), drug targeting efficiency (DTE) and biodistribution studies in different organs including brain. The radiolabeling efficiency of DLX and DLX-NLC was found to be 98.41 ± 0.96 and 98.87 ± 0.82 after 30 min, respectively. The biodistribution studies exhibited higher percentage of radioactivity/g for DLX-NLC formulations in brain as compared with the DLX. The higher DTP (86.80%) and DTE (757.74%) suggested that DLX-NLC formulation has a better brain targeting efficiency than DLX solution (DTP=65.12%; DTE=287.34%) when administered intranasally. Moreover, the intranasal administration exhibited about 8-times higher concentration of DLX in brain when compared with the intravenous administration of DLX solution. The intranasal NLC containing DLX can be employed as an effective method for the treatment of depression.

Pharmacotherapy for mood disorders in pregnancy: a review of pharmacokinetic changes and clinical recommendations for therapeutic drug monitoring

OBJECTIVE

Pharmacotherapy for mood disorders during pregnancy is often complicated by pregnancy-related pharmacokinetic changes and the need for dose adjustments. The objectives of this review are to summarize the evidence for change in perinatal pharmacokinetics of commonly used pharmacotherapies for mood disorders, discuss the implications for clinical and therapeutic drug monitoring (TDM), and make clinical recommendations.

METHODS

The English-language literature indexed on MEDLINE/PubMed was searched for original observational studies (controlled and uncontrolled, prospective and retrospective), case reports, and case series that evaluated or described pharmacokinetic changes or TDM during pregnancy or the postpartum period.

RESULTS

Pregnancy-associated changes in absorption, distribution, metabolism, and elimination may result in lowered psychotropic drug levels and possible treatment effects, particularly in late pregnancy. Mechanisms include changes in both phase 1 hepatic cytochrome P450 and phase 2 uridine diphosphate glucuronosyltransferase enzyme activities, changes in hepatic and renal blood flow, and glomerular filtration rate. Therapeutic drug monitoring, in combination with clinical monitoring, is indicated for tricyclic antidepressants and mood stabilizers during the perinatal period.

CONCLUSIONS

Substantial pharmacokinetic changes can occur during pregnancy in a number of commonly used antidepressants and mood stabilizers. Dose increases may be indicated for antidepressants including citalopram, clomipramine, imipramine, fluoxetine, fluvoxamine, nortriptyline, paroxetine, and sertraline, especially late in pregnancy. Antenatal dose increases may also be needed for lithium, lamotrigine, and valproic acid because of perinatal changes in metabolism. Close clinical monitoring of perinatal mood disorders and TDM of tricyclic antidepressants and mood stabilizers are recommended.

Pharmacokinetic considerations for therapies used to treat interstitial cystitis

INTRODUCTION

Interstitial cystitis (IC) or bladder pain syndrome (BPS) is defined as supra-pubic pain related to bladder filling. IC is characterized by a particular symptom complex with no identifiable causes; as with bladder hypersensitivity it is usually associated with urinary frequency and urgency with bladder pain. No current treatments have a significant impact on symptoms over time.

AREAS COVERED

This systematic review examines the pharmacokinetic aspects and adverse event of present IC therapy to highlight appropriate treatment to improve the symptoms of IC. This article reviews material obtained via Medline, PubMed, and EMBASE literature searches up to October 2013.

EXPERT OPINION

The correct approach to IC should consider a multidisciplinary team of specialists and a multimodal treatment package that include psychotherapy, behavior change, physical activation, and analgesic treatment. Unfortunately, a single therapeutic target for IC is not yet known. With regard to pathophysiology and therapy, there is more to discover. The first insult damages the bladder urothelium, hence vehicles that lead the drug to penetrate the wall of the bladder might be a novel strategic approach.

Effects of duloxetine on norepinephrine and serotonin transporter activity in healthy subjects

Duloxetine selectively inhibits the serotonin (5-HT) and norepinephrine (NE) transporters (5-HTT and NET, respectively), as demonstrated in vitro and in preclinical studies; however, transporter inhibition has not been fully assessed in vivo at the approved dose of 60 mg/d. Here, the in vivo effects of dosing with duloxetine 60 mg once daily for 11 days in healthy subjects were assessed in 2 studies: (1) centrally (n = 11), by measuring concentrations of 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylglycol (DHPG), and NE in cerebrospinal fluid, and (2) versus escitalopram 20 mg/d (n = 32) in a 2-period crossover study by assessing the ΔDHPG/ΔNE ratio in plasma during orthostatic testing and by pharmacokinetic/pharmacodynamic modeling of reuptake inhibition using subjects' serum in cell lines expressing cloned human 5-HTT or NET. At steady state, duloxetine significantly reduced concentrations of DHPG and 5-hydroxyindoleacetic acid (P < 0.05), but not NE, in cerebrospinal fluid; DHPG was also decreased in plasma and urine. The ΔDHPG/ΔNE ratio in plasma decreased significantly more with duloxetine than escitalopram (65% and 21%, respectively; P < 0.0001). Ex vivo reuptake inhibition of 5-HTT was comparable (EC50 = 44.5 nM) for duloxetine and escitalopram, but duloxetine inhibited NET more potently (EC50 = 116 nM and 1044 nM, respectively). Maximal predicted reuptake inhibition for 5-HTT was 84% for duloxetine and 80% for escitalopram, and that for NET was 67% and 14%, respectively. In summary, duloxetine significantly affected 5-HT and NE turnover in the central nervous system and periphery; these effects presumably occurred via inhibition of reuptake by the 5-HTT and NET, as indicated by effects on functional reuptake inhibition ex vivo.

Duloxetine: a review of its use in the management of major depressive disorder in older adults

Duloxetine (Cymbalta(®)) is a selective serotonin norepinephrine reuptake inhibitor indicated for the treatment of major depressive disorder (MDD). This article reviews the therapeutic efficacy and tolerability of duloxetine in older adults with MDD and summarizes its pharmacological properties. Treatment with duloxetine significantly improved several measures of cognition, depression, anxiety, pain and health-related quality-of-life (HR-QOL) in older adults with MDD in two 8-week, double-blind, placebo-controlled trials. However, no significant improvements in measures of depression were observed at week 12 (primary endpoint) of a 24-week, double-blind trial, although symptoms of depression did improve significantly at earlier timepoints. Benefit of treatment was also observed during continued therapy in the 24-week study (i.e. after the 12-week primary endpoint) and in an open-label, 52-week study, with improvements being observed in some measures of depression, pain and HR-QOL. Duloxetine was generally well tolerated in these studies, with nausea, dizziness and adverse events reflecting noradrenergic activity (e.g. dry mouth, constipation) being the most common treatment-emergent adverse events during treatment for up to 52 weeks. Duloxetine therapy had little effect on cardiovascular parameters and bodyweight. Although further well designed and long-term studies in this patient population are required to confirm the efficacy of duloxetine and to compare it with that of other antidepressants, current evidence suggests that treatment with duloxetine may be beneficial in older adults with MDD.

Identification of RC-33 as a potent and selective σ1 receptor agonist potentiating NGF-induced neurite outgrowth in PC12 cells. Part 2: g-scale synthesis, physicochemical characterization and in vitro metabolic stability

Strong pharmacological evidences indicate that σ1 receptors are implicated in the pathophysiology of all major CNS disorders. In the last years our research group has conducted extensive studies aimed at discovering novel σ1 ligands and we recently selected (R/S)-RC-33 as a novel potent and selective σ1 receptor agonist. As continuation of our work in this field, here we report our efforts in the development of this new σ1 receptor agonist. Initially, we investigated the binding of (R) and (S) enantiomers of RC-33 to the σ1 receptor by in silico experiments. The close values of the predicted affinity of (R)-RC-33 and (S)-RC-33 for the protein evidenced the non-stereoselective binding of RC-33 to the σ1 receptor; this, in turn, supported further development and characterization of RC-33 in its racemic form. Subsequently, we set-up a scaled-up, optimized synthesis of (R/S)-RC-33 along with some compound characterization data (e.g., solubility in different media and solid state characterization by thermal analysis techniques). Finally, metabolic studies of RC-33 in different biological matrices (e.g., plasma, blood, and hepatic S9 fraction) of different species (e.g., rat, mouse, dog, and human) were performed. (R/S)-RC-33 is generally stable in all examined biological matrices, with the only exception of rat and human liver S9 fractions in the presence of NADPH. In such conditions, the compound is subjected to a relevant oxidative metabolism, with a degradation of approximately 65% in rat and 69% in human. Taken together, our results demonstrated that (R/S)-RC-33 is a highly potent, selective, metabolically stable σ1 agonist, a promising novel neuroprotective drug candidate.